CH Patent 698837 discloses the fabrication of a timepiece component by micromachining a water of amorphous or crystalline material, such as crystalline or polycrystalline silicon.
Such micromachining is generally obtained by deep reactive ion etching (also known by the abbreviation “DRIE”). As illustrated in FIGS. 1 to 3, a known micromachining method consists in structuring a mask 1 on a substrate 3 (cf. FIG. 1, step A) followed by a “Bosch” deep reactive ion etching combining in succession an etching phase (cf. FIG. 1, steps B, D, E) followed by a passivation phase (cf. FIG. 1, step C, layer 4) in order to obtain from the pattern of mask 1, an anisotropic, i.e. substantially vertical, etch 5, in the wafer (cf. FIG. 2).
As illustrated in FIG. 3, an example of a “Bosch” deep reactive ion etching is shown with, in solid lines, the flow of SF6 in sccm as a function of time in seconds, for etching a silicon wafer and, in dotted lines, the flow of C4F8 in sccm as a function of time in seconds, for the passivation, i.e. the protection, of the silicon wafer. It is thus clearly seen that the phases are strictly consecutive and each have a specific flow and time.
In the example of FIG. 3, there is shown a first etching phase G1, with a flow of SF6 at 300 sccm for 7 seconds, followed by a first passivation phase P1 with a flow of C4F8 at 200 sccm for 2 seconds, followed by a second etching phase G2 with a flow of SF6 at 300 sccm for 7 seconds again, and finally, followed by a second passivation phase P2 with a flow of C4F8 at 200 sccm for 2 seconds again, and so on. It is thus noted that a certain number of parameters enable the “Bosch” deep reactive ion etch process to be varied to obtain more or less marked scalloping in the wall of vertical etch 5.
After several years of fabrication, it was found that these vertical etches 5 were not entirely satisfactory, particularly as regards tribology.